1. Field of the Invention
The invention relates to an automatic roll-up device for a safety belt having a device for blocking the belt band in case of danger, which device is automatically activated when a predetermined acceleration or deceleration of the vehicle is exceeded.
2. Description of the Prior Art
In the known roll-up automatic roll-up devices for safety belts, (U.S. Pat. No. 3,901,459) a wind-up spring is arranged at one side of the belt shaft which is supported in a stable housing, while the opposite shaft end is in connection with a detenting locking device and with a release mechanism. In case of danger, for example, in case of a crash, the release mechanism (activating sensor), which is provided with an inertia mass, acts on a control disc, and the control disc effects the complete blocking of the belt shaft and, thereby, of the belt by means of the detenting locking device. Hereby, the total pulling forces act on the detenting locking device and also on the belt shaft when the device is blocked, so that these parts must be made very strong and massive, to be capable of withstanding the extremely large pull-forces in case of danger. This strong system is uneconomical with respect to construction and cost, and furthermore, suffers from its high inertia, whereby the normal motion of the safety belt is made more difficult, and the reaction time of the safety belt is increased.
On the other hand, braking- or clamping devices for safety belts are known (Great Britain Patent Specification No. 1 416 517, German Published Non-Prosecuted Application No. 19 49 061), wherein the belt band is deflected over several braking rollers, so that the belt is braked by the thereby generated high friction forces when a pulling force is acting on the belt, or wherein at a certain acceleration of the belt, the belt is mechanically strongly pressed between clamping jaws or clamping rollers, and is in this manner prevented from being pulled out further. In both cases there is no assurance that the belt which is in tension is actually also blocked (arrested) within a very short time span, and reliably prevented from being pulled out any further.